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Anatomy of the CMC Joint

(See also: CMC arthritis)


  • base of thumb metacarpal articulates w/ saddle shaped trapezium;
  • saddle shaped articulation provides inherent stability;
  • radial lateral ligament, which is covered by APL tendon, inserts into the thumb metacarpal;

deep anterior oblique ligament (palmar beak ligament)

  • originates on the tuberosity of the trapezium & insertes on ulnar and volar edge of metacarpal base;
  • anterior oblique ligament provides mobility but prevents dislocation;
  • ligament maintains volar stability of saddle joint;
  • anchors volar lip of first metacarpal to trapezium and second metacarpal;
  • maximum tension occurs in this ligament with the metacarpal in flexion, abduction, and supination;
  • traditionally, it is thought that insufficiency of this ligament leads to basal joint arthritis;
  • ligament may help function as a pivot for the first metacarpal during palmar abduction to allow pronation;

dorsal radial capsular ligament

  • is covered by EPB & EPL;
  • some consider this ligament to be more important than the volar ligament;
  • sectioning of this ligament produces dorsoradial subluxation of the thumb metacarpal;

ulnar ligament;

  • limits range of abduction & extension of thumb
  • if this ligament is torn unopposed pull of APL & EPL & EPB muscles dislocates metacarpal shaft radially and proximally